1. Field of the Invention
The present invention relates to wafer heaters for use in semiconductor-producing apparatus, heating units using such wafer heaters, and processes for producing such heaters. The heating unit is to be used for a pressure-reduced CVD apparatus or a photoetching apparatues for the production of films on surfaces of silicon wafers in the semiconductor industry.
2. Related Art Statement
In the CVD necessitating super cleanness, a corrosive gas such as a chlorine based gas or a fluorine based gas is used as a deposting gas, an etching gas or a cleaning gas. Thus, when a conventional heater in which the surface of a resistance heating element is coated with a metal such as stainless steel or Inconel is used as a heater for heating a wafer in such a state that it is brought into contact with this corrosive gas, particles of a chloride, a fluoride, an oxide or the like having a particle diameter of few to several .mu.m are unfavorably formed on the surface of a heater upon exposure to the corrosive gas.
Under the circumstances, an indirectly heating type wafer heater shown in FIG. 1 has been developed. In this heater, infrared lamps 101 are disposed outside a chamber 102 which is exposed to a depositing gas or the like, an infrared ray-permeable window 103 is provided in an outer wall 104 of the chamber, and a wafer placed on an upper surface of a heating member 105 of a corrosion resistive material such as graphite is heated by irradiating infrared rays upon the heating member 5. As compared with a directly heating type, the indirectly heating type heater has greater heat loss, and requires longer tame for raising the temperature. Further, transmission of the infrared rays is gradually interrupted with attachment of a CVD film onto the infrared ray-permeable window 103, so that heat is absorbed by the infrared ray-permeable window 103 to overheat the window.